Write the chemical formula of Sodium zincate in a step-by-step manner.

Step 1 — Write each symbol with its valency

$\text{Na}^{1+} \phantom{\nearrow} \text{ZnO}_2^{2-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{ZnO}$2} \Rightarrow \underset{\phantom{1}{2}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{ZnO}2} \\[0.5em]

Step 3 — Write the interchanged number & hence the formula

Therefore, we get

Formula of Sodium zincate : $\bold{Na$2ZnO2}